RexTalionis:Headso: they need to close the place for that until some guy can get around to pressure washing it off?

The federal government doesn't even recommend using pressure washers to wash marble headstones in government cemeteries (Arlington, for instance).

ncptt.nps.gov/wp-content/uploads/Best-Practices-Final.pdf

What are the chances they would be willing to use pressure washer to clean a national monument?

Absolutely zero.They'll first have a team of Ph.D. contractors do an analysis of the damage, which will take three years and force the entire monument to be closed. Then, another contractor will come in and cut out the damaged pieces and new pieces will be carved from the same limestone or marble that was originally used. That will take five years. The the new pieces will be installed, which will take until 2024.Everybody gets paid.